Furan and its derivatives are useful precursors for industrial chemicals in the area of, for example, pharmaceuticals, herbicides and polymers. Furan may be converted into tetrahydrofuran (THF) and 1,4-butanediol (1,4-BDO). THF and 1,4-BDO are valuable chemicals used industrially as solvents and in the production of elastic fibres such as elastane/spandex, polybutyrate terephthalate and derivatives of gamma butyrolactone.
These chemicals are usually produced industrially via a number of routes from petrochemical feedstocks, obtainable from fossil fuels. One industrial route for the production of 1,4-BDO requires the reaction of acetylene with two equivalents of formaldehyde followed by hydrogenation of the resultant 1,4-butynediol to form 1,4-butanediol. In an alternative process, propylene oxide is converted to allyl alcohol. The allyl alcohol is then hydroformylated to form 4-hydroxybutyraldehyde, which may be hydrogenated to form 1,4-butanediol. Other traditional routes use butadiene, allyl acetate or succinic acid as starting materials. 1,4-butanediol may also be produced as a side-product in a method for making tetrahydrofuran (THF) by oxidizing n-butane to crude maleic anhydride followed by catalytic hydrogenation.
In recent years, increased efforts have focused on producing chemicals, including 1,4-BDO and THF, from renewable feedstocks, such as sugar-based materials.
A method for obtaining furan from non-fossil fuel based sources involves the decarbonylation of furfural. Examples of reaction processes for achieving this and the subsequent conversion of the furan into its derivatives can be found in Hoydonck, H E; Van Rhijn, W M; Van Rhijn, W; De Vos, D E; & Jacobs, P A; (2012) Furfural and Derivatives, in Ullmann's Encyclopedia of Industrial Chemistry (volume 16, pp 285-313), Wiley-VCH Verlag GmBH & Co. KGaA, Weinheim; Dunlop, A P; and Peters, F N; in The Furans Reinhold Publ. Co, 1953; K. J. Zeitsch, in “The Chemistry and Technology of Furfural and its Many By-products” Sugar Series 13, Elsevier, 2000; Lange, J-P; van der Heide, E; van Buijtenen, J; and Price, R; Furfural—A Promising Platform for Lignocellulosic Biofuels; ChemSusChem 2012, 5, 150-166 and Watson, J. M.; Ind. Eng. Chem. Prod. Res. Develop., 1973, 12(4), 310. Furfural may be obtained from hemicellulose via acid hydrolysis in the liquid phase as well as in the gas phase as described in WO 2002/22593 and WO 2012/041990.
The conversion of furan to THF and 1,4-BDO by hydrogenation in the presence of water, acetic acid and Raney nickel or oxide supported nickel catalyst is described in Watson, J M; Ind. Eng. Chem. Prod. Res. Develop., 1973, 12(4), 310.
A process for the conversion of furan into 1,4-BDO and THF is taught in U.S. Pat. No. 5,905,159. This document teaches a process in which furan is converted as a reaction mixture with water and in the presence of hydrogen but in the absence of a water-soluble acid in a single stage over a hydrogenation catalyst. The hydrogenation catalyst of U.S. Pat. No. 5,905,159 contains at least one element of subgroup I, V, VI, VII or VIII in the form of a compound or in elemental form, with the restriction that the catalyst does not contain nickel alone being applicable. The preferred catalyst in this process is Re/Ru on active carbon. A similar catalyst is used in the process described in Pan, T; Deng, J; Xu, Q; Zuo, Y; Guo, Q-X and Fu, Y; Catalytic Conversion of Furfural into a 2,5-Furandicarboxylic Acid-based Polyester with Total Carbon Utilisation; ChemSusChem 2013, 6, 47-50.
Known methods in the art provide a mixture of THF, 1,4-BDO and n-butanol. Such methods generally provide THF when using a catalyst without rhenium as a promoter. The use of Re as a promoter can increase the selectivity to 1,4-BDO. However, rhenium is a rare and expensive metal.
It would be advantageous to provide a method for the production of 1,4-butanediol and tetrahydrofuran from furan in which the amount of 1,4-BDO is maximised, without using rhenium as a promoting metal on the catalyst.